The pressure filter consists of a fabric that runs back and forth inside the filter. The concentrate sludge is fed to the planes formed between the fabric belts. Once the sludge has been fed to the plane, the so-called filter chamber, the first compression phase begins. The filter is pressed tightly and the sludge in the filter chamber is pressed against the filter fabric, forming a so-called sludge cake. A washing solution is then fed into the filter chamber, which is also compressed in the same way as the sludge. Finally, the sludge cake is dried with compressed air. Compressed air also removes the last drops of water from the filter chamber. After the drying, the plates open and the sludge cake is removed by rotating the fabric forward.

The vertical model of the pressure filter, which is more efficient than the folded model, was originally invented in the Soviet Union. In 1972, the Lappeenranta workshop bought a license to produce and develop a vertical pressure filter.

In the Vuonos and Keretti mines, experiments were carried out with pressure filters, but it was decided not to use them in production.